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Post by Karl L on Jan 16, 2023 6:54:28 GMT -8
Hi Trev, I'm doing a careful re-check of various things before going any further with my 125mm design. Looking at the Sketchup and notes on page 1 of this thread, the basic firebox for a 150mm system is 305mm wide and 305mm tall. But looking at the photo in this post, it looks significantly taller (from the top of the box to bottom of 'V') than it is wide: donkey32.proboards.com/post/36830/threadIs that just distortion in the photo? Thanks, Karl
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Post by Karl L on Jan 15, 2023 4:05:18 GMT -8
What is the chimney like? It's currently about 8m, unlined stone... But it will be 2m of insulated flue, measured from bottom of stove's internal chimney, then some kind of bend (45 degrees?) and through the wall into the stone chimney. My stove has 3.267 m2 of ISA, but the shortest gasflow path from the afterburner is about 13 feet / 4 meters to the bottom of the internal chimney. I prefer the smaller gaps in the firebricks, the latest one really looks like it'll favor the first few. I'd make it so you can easily experiment and see what works best. Yes, one of the advantages of this design is it will be easy to change the internal configuration. I don't know what effect it will have, but the shortest gasflow path from the square exit port to the bottom of the internal chimney in this design is ~1.3m. Even with the wider gaps in the firebricks the total path lengths for all the vertical channels are very similar: e.g. if the gas goes down the first channel it is forced to take the longest path to the chimney at the bottom of the stove. So I would expect the flow to be roughly equal for all the vertical channels. But the only way to be sure is to try it...
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Post by Karl L on Jan 13, 2023 9:58:35 GMT -8
And I guess it may be possible to 'tune' the overall gas flow resistance and heat extraction to suit the chimney, by pairing some brick-stacks and not others...
This tuning could be done within the same overall envelope - i.e. without having to make a new steel box.
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Post by Karl L on Jan 13, 2023 9:35:12 GMT -8
Here's a version with pairs of brick-stacks moved together: Magnetite mass v5I think the ISA is around 3m2, depending on whether the layer of bricks over the top is counted twice (like the top of a bell), whether I let gas through the outsides of the first and last brick-stacks, and whether the sides of the horizontal channels are insulating material or not. I am happy to have a lower ISA than standard, just in case my chimney draft isn't strong enough.
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Post by Karl L on Jan 13, 2023 8:36:08 GMT -8
I have two concerns with the design: 1) don't you get your bell dirty from smokes? How do you clean the gap between the bricks? 2) do you have some experience regarding ISA of such a bell? May be the exchange area is a little too big. According existing design rules (3.7m2 for a 125cm system), you should reduce the number of rows by ~ 30%.
Thanks Trev and Fedia :-) To clean the gaps, I think I can take off the top and then use a radiator-cleaning brush in the gaps. Then put a vacuum cleaner into a clean-out door at the side of the stove (not shown in the Sketchup yet). Re. Trev's concern about too much resistance to gas flow, and Fedia's concern about too much heat extraction: moving pairs of brick-stacks together would make wider channels and also reduce the contact area, decreasing both resistance and heat extraction: If the internal surface area for heat collection is too high (i.e it extracts too much heat from the gas), the stacks can rebuilt into a lower surface area configuration -- e.g. by moving pairs of stacks together.
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Post by Karl L on Jan 13, 2023 2:32:24 GMT -8
I've modified the gas path so that every vertical channel has a very similar overall path length from the core to the exit flue, at the cost of extending the top and bottom horizontal path lengths a bit. The top channel is mostly 1.8 System CSA, but that could be increased quite easily. Here's the new Sketchup: Magnetite mass v4
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Post by Karl L on Jan 12, 2023 23:58:31 GMT -8
I realised the total CSA of the channels I gave (4.5 x System and 6 x System, depending on spacing) are for my current 115mm system.
For a 125mm system they are around 3.8 x System and 5.1 x System.
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Post by Karl L on Jan 12, 2023 14:15:57 GMT -8
Thanks Trev,
The total CSA of the channels is over 47,000 mm2 - which is about 4.5 times the notional system CSA, I think. It would be quite easy to get the CSA up to 6 x System just by widening the channels a bit (which would another 50mm to the overall width of the stove) or by removing 6 bricks.
What multiple of System CSA would present a low enough resistance, do you think ?
Re. the closer channels being favoured:
Yes, I was wondering about that.
I was thinking that if some channels were favoured then they would heat up more, and this would increase the resistance to flow down those channels for two reasons:
1) The gas would remain hotter -- and so more buoyant -- than in the unfavoured (and so cooler) channels.
2) The hotter gas would also have higher volume, making it harder get through the channel.
I guess it might also be possible to roughly equalise the resistance of the channels by having smaller channel widths closer to the core, and/or changing the route from the bottom of the channels to the exit flue.
(Thanks for the ash box suggestion - I forget to put it in the Sketchup - that's corrected now).
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Post by Karl L on Jan 12, 2023 6:52:27 GMT -8
I'm thinking about possible alternative mass configurations for a vortex-core stove. One idea I had was to arrange storage heater bricks in vertical stacks with gas flow 'slots' in-between each stack. It's essentially a lot of parallel vertical contraflow channels. I've done a sketch of the idea in Sketchup, here: Magnetite mass v3This is a 125mm sized system, with correspondingly less mass and less internal surface area than Trev's original 150mm system. There is no cook top, so I've put some mass in that position instead, and maybe I'll put some insulation over that. This arrangement has a high surface area and a short gas path length. The total gas flow cross sectional area, down through the slots, can be adjusted at design time to some multiple of the system size. If the internal surface area for heat collection is too high (i.e it extracts too much heat from the gas), the stacks can rebuilt into a lower surface area configuration -- e.g. by moving pairs of stacks together. Are there any problems with this configuration that anyone can see? What total cross sectional area would be needed for the slots? Thanks!
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Post by Karl L on Oct 27, 2022 1:29:04 GMT -8
Thanks for all that information and experience, Forsythe. I've asked for the datasheet for that particular product to find out more...
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Post by Karl L on Oct 26, 2022 10:00:43 GMT -8
Thanks, Dan. Did you have any experience of what kind of fumes are given off when the binder is burnt off? In the use I am thinking of, these fumes would enter the living space.
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Post by Karl L on Oct 25, 2022 8:50:19 GMT -8
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Post by Karl L on Oct 20, 2022 23:00:28 GMT -8
Trev, I'd like to understand the gas flow through the mass for the most recent iteration of your stove - can you point me to where in this thread I might see that? Thanks
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Post by Karl L on Oct 20, 2022 5:41:53 GMT -8
6 meters is a good length chimney, mine is only a bit under 4 meters from the bottom of the stove to the top of the cowl. Thanks - is your chimney lined or unlined?
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Post by Karl L on Oct 19, 2022 11:28:32 GMT -8
The next thing I want to do is improve the flue a little by insulating some of the length -- I can only do the first 2m -- and then add a bigger mass with 3.0 msq ISA and maybe 600Kg mass.
Because of the poor flue I guess it will have to be a bell of some kind.
I think I will have to avoid building the bell in front of an exiting fireplace opening, just in case the stove produces enough soot, etc, over a long period, that I need to sweep the chimney.
Or maybe I can design the mass so it can be easily deconstructed after the first season, to check/sweep the flue?
Trev - for that second option I am interested in how you built your mass. It looks like steel sheets and steel angle without any gas- or water-tight seals at the edges -- is that right? I think you would have said if you had any exhaust leaks or condensate leaks.
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